In recent years, various information services (data, sound, broadcasting, wireless data, and the like) using an access network between subscribers and a station have been widely provided. With wide-spreading of these information services, usage of a P2MP (Point-to-Multi Point) PON (Passive Optical Network) system, which realizes inexpensive and stable high bandwidth communication even if subscribers are away from a station, has been widespread as an alternative to xDSLs (Digital Subscriber Lines), which is a transfer method using a metal line.
In commercial access networks using the PON system, there have been services of a GE (Gigabit Ethernet®)-PON (see Non Patent Literature 1 mentioned below), in which WDM (Wave Division Multiplexing) that is capable of performing two-way communication with one optical fiber transfer line is used. Furthermore, in GE PONS, TDM (Time Division Multiplexing) is applied to a downlink (OLT (Optical Line Terminal)→ONU (Optical Network Unit)) and TDMA (Time Division Multiple Access) is applied to an uplink (ONU→OLT).
Further, development of a 10 G-EPON (see Non Patent Literature 2 mentioned below) having a bit rate 10 times faster than that of the GE-PON has been in progress while applying a high-speed TDM technique.